The apparatus of this invention uses some of the principles recited in U.S. Pat. No. 4,436,423.
A ring laser gyroscope generally includes mirrors for reflecting laser beams along a laser cavity. The laser cavity is frequently triangular or rectangular, and the mirrors are positioned at the intersections of the straight portions of the cavity. Because of irregularities on the surfaces of the mirrors, a beam impinging upon a particular mirror is not perfectly reflected. Rather, some back-scattering occurs. This causes errors in the gyro at high rotation rates and also causes the beat frequency between two beams in the gyroscope to disappear at low inertial rotation input rates. Such disappearance is called lock-in which has been recognized for some time in the prior art and has been solved by driving the gyroscope body in rotational oscillation or dither. The means for accomplishing the dither conventionally includes a piezoelectric actuator connected to a suspension for the gyroscope to oscillate the body. The frequency of oscillation is frequently at the suspension's natural mechanical resonant frequency. The dither is superimposed upon the actual rotation of the gyroscope in inertial space. Various techniques have evolved to recover inertial rotation data free from dither, but such is not part of this invention.